Stimulus-frequency Otoacoustic Emissions Research Articles

Otoacoustic emissions in African mole-rats

African mole-rats display highly derived hearing that is characterized by low sensitivity and a narrow auditory range restricted to low frequencies < 10 kHz. Recently, it has been suggested that two species of these rodents do not exhibit distortion product otoacoustic emissions (DPOAE), which was interpreted as evidence for a lack of cochlear amplification. If true, this would make them unique among mammals. However, both theoretical considerations on the generation of DPOAE as well as previously published experimental evidence challenge this assumption. We measured DPOAE and stimulus-frequency otoacoustic emissions (SFOAE) in three species of African mole-rats (Ansell's mole-rat - Fukomys anselli; Mashona mole-rat - Fukomys darlingi; naked mole-rat - Heterocephalus glaber) and found unexceptional otoacoustic emission values. Measurements were complicated by the remarkably long, narrow and curved external ear canals of these animals, for which we provide a morphological description. Both DPOAE and SFOAE displayed the highest amplitudes near 1 kHz, which corresponds to the region of best hearing in all tested species, as well as to the frequency region of the low-frequency acoustic fovea previously described in Ansell's mole-rat. Thus, the cochlea in African mole-rats shares the ability to generate evoked otoacoustic emission with other mammals.

Deep Learning Models for Predicting Hearing Thresholds Based on Swept-Tone Stimulus-Frequency Otoacoustic Emissions.

This study aims to develop deep learning (DL) models for the quantitative prediction of hearing thresholds based on stimulus-frequency otoacoustic emissions (SFOAEs) evoked by swept tones. A total of 174 ears with normal hearing and 388 ears with sensorineural hearing loss were studied. SFOAEs in the 0.3 to 4.3 kHz frequency range were recorded using linearly swept tones at a rate of 2 Hz/msec, with stimulus level changing from 40 to 60 dB SPL in 10 dB steps. Four DL models were used to predict hearing thresholds at octave frequencies from 0.5 to 4 kHz. The models-a conventional convolutional neural network (CNN), a hybrid CNN-k-nearest neighbor (KNN), a hybrid CNN-support vector machine (SVM), and a hybrid CNN-random forest (RF)-were individually built for each frequency. The input to the DL models was the measured raw SFOAE amplitude spectra and their corresponding signal to noise ratio spectra. All DL models shared a CNN-based feature self-extractor. They differed in that the conventional CNN utilized a fully connected layer to make the final regression decision, whereas the hybrid CNN-KNN, CNN-SVM, and CNN-RF models were designed by replacing the last fully connected layer of CNN model with a traditional machine learning (ML) regressor, that is, KNN, SVM, and RF, respectively. The model performance was evaluated using mean absolute error and SE averaged over 20 repetitions of 5 × 5 fold nested cross-validation. The performance of the proposed DL models was compared with two types of traditional ML models. The proposed SFOAE-based DL models resulted in an optimal mean absolute error of 5.98, 5.22, 5.51, and 6.06 dB at 0.5, 1, 2, and 4 kHz, respectively, superior to that obtained by the traditional ML models. The produced SEs were 8.55, 7.27, 7.58, and 7.95 dB at 0.5, 1, 2, and 4 kHz, respectively. All the DL models outperformed any of the traditional ML models. The proposed swept-tone SFOAE-based DL models were capable of quantitatively predicting hearing thresholds with satisfactory performance. With DL techniques, the underlying relationship between SFOAEs and hearing thresholds at disparate frequencies was explored and captured, potentially improving the diagnostic value of SFOAEs.

Otoacoustic emissions reveal the micromechanical role of organ-of-Corti cytoarchitecture in cochlear amplification

The intricate, crystalline cytoarchitecture of the mammalian organ of Corti presumably plays an important role in cochlear amplification. As currently understood, the oblique, Y-shaped arrangement of the outer hair cells (OHCs) and phalangeal processes of the Deiters cells serves to create differential "push-pull" forces that drive the motion of the basilar membrane via the spatial feedforward and/or feedbackward of OHC forces. In concert with the cochlear traveling wave, the longitudinal separation between OHC sensing and forcing creates phase shifts that yield a form of negative damping, amplifying waves as they propagate. Unlike active forces that arise and act locally, push-pull forces are inherently directional-whereas forward-traveling waves are boosted, reverse-traveling waves are squelched. Despite their attractions, models based on push-pull amplification must contend with otoacoustic emissions (OAEs), whose existence implies that amplified energy escapes from the inner ear via mechanisms involving reverse traveling waves. We analyze hybrid local/push-pull models to determine the constraints that reflection-source OAEs place on the directionality of cochlear wave propagation. By implementing a special force-mixing control knob, we vary the mix of local and push-pull forces while leaving the forward-traveling wave unchanged. Consistency with stimulus-frequency OAEs requires that the active forces underlying cochlear wave amplification be primarily local in character, contradicting the prevailing view. By requiring that the oblique cytoarchitecture produce predominantly local forces, we reinterpret the functional role of the Y-shaped geometry, proposing that it serves not as a push-pull amplifier, but as a mechanical funnel that spatially integrates local OHC forces.

Temporal dynamics of the medial olivocochlear reflex in humans

Ipsilateral and contralateral sounds can activate the medial olivocochlear reflex. The time course of medial efferent effects could contribute to the binaural unmasking of sounds. Computational modeling suggests that implementing efferent time constants improves speech-in-noise recognition. In addition, the time course could also support the protective function offered by the medial efferents. However, the current knowledge of efferent time constants is limited to a few probe frequencies (e.g., 1000 Hz) in limited subjects. The time course of medial efferent activation might be different for other probe frequencies or elicitors. In this study, the time course of the medial olivocochlear reflex was measured using stimulus frequency otoacoustic emissions recorded at spectral peaks near 1000 and 4000 Hz with broadband elicitors in 17 normal-hearing adults. Several preliminary but important findings emerged: (1) The onset response could be fitted with fast, medium, and/or slow time constants for limited subjects; (2) The magnitude (30–40%) of the efferent effect was similar to those reported in the literature; (3) The overall decay time appears to be longer for 4000 Hz relative to 1000 Hz; and (4) There was large individual variability in all response parameters across subjects. These findings will be discussed in detail. [Work supported by NIH/NIDCD R01DC018046.]

A fast algorithm for the measurement of stimulus-frequency otoacoustic emission suppression tuning curves based on multi-level swept suppressor tones

Algorithms for measuring stimulus-frequency otoacoustic emission (SFOAE) suppression tuning curves (STCs) typically use pure tones as suppressors, leading to procedures which are time-consuming and difficult to apply in clinical settings. A fast algorithm based on multi-level swept suppressor tones (MLSST) is proposed in this study. Taking advantage of the time-varying frequencies of swept tones, the suppression effects on SFOAE produced by swept suppressor tones are obtained within a single test. Further, a SFOAE STC may be extracted by interpolation from a set of suppression-effect functions at multiple suppressor levels. In the present study, SFOAE STCs were obtained in twenty-six normal-hearing subjects using the fast MLSST and the traditional pure-tone algorithms. SFOAE STCs were measured with high test–retest repeatability using the MLSST algorithm (average mean absolute errors of 2.12 dB) and were nearly consistent with the SFOAE STCs obtained by the pure-tone algorithm (average mean absolute errors of 3.13 dB). In addition, with>1.8 times frequency solution of the acquired curves, the measurement speed of our MLSST algorithm was approximately 2.14 times faster than the traditional one.

Long-latency component of stimulus frequency otoacoustic emissions: Relationship to behavioral measures

Uncertainties regarding the generation mechanism and source of human stimulus frequency otoacoustic emissions (SFOAEs), as well as the possible generation of artifacts, have previously restricted the use of SFOAEs in clinical settings for assessing cochlear function. Over the years, advanced time-frequency analysis of SFOAEs, using models of SFOAE delays as a function of frequency, have been implemented in an effort to isolate the long-latency (LL) component of SFOAEs—improving the signal-to-noise ratio and the artifact rejection as noteworthy byproducts. In order to test the hypothesis that behavioral measures and SFOAE LL component both reflect the activity of limited cochlear regions, the relationship between SFOAE LL component and behavioral measures was investigated. SFOAEs, behavioral thresholds and psychophysical tuning curves (PTCs) were measured for probe frequencies centered around 0.75, 1, 2, 4, 8, 10, 12.5 and 14 kHz. Stimulus levels for PTCs (10 dB SL) and SFOAEs (10, 20 and 30 dB SL) were referenced to behavioral thresholds at each frequency. Using the same in situ calibration technique using Thevenin-equivalent source parameters, behavioral thresholds and SFOAE-estimated thresholds from input-output functions of the SFOAE LL component were strongly correlated. Furthermore, there was a strong correlation between SFOAE-based and psychophysical tuning estimates.

Cross-species characterization of joint otoacoustic emission profiles in sensorineural hearing loss

Current clinical assessment of otoacoustic emissions (OAEs) is typically limited to presence or absence of emissions to detect hearing loss, but recent work suggests advanced analyses and data collection methods have the potential to improve the diagnostic utility of OAEs. OAEs arise from two distinct mechanisms, nonlinear distortion and linear reflection, which are both sensitive to the health of outer hair cells but may reflect separate aspects of cochlear mechanical function. Joint distortion-reflection OAE profiles offer a non-invasive characterization of peripheral auditory physiology and dysfunction (Abdala and Kalluri, 2017). In this study, swept-tone distortion-product OAEs were separated into distortion and reflection components. Swept-tone stimulus-frequency OAEs, reflection-type emissions, were measured using a suppressor paradigm. Joint OAE profiles will be estimated for multiple pre-clinical chinchilla models of sensorineural hearing loss (SNHL) and in humans with either normal hearing or sensorineural hearing loss. In chinchillas, we expect SNHL models with distinct profiles of cochlear damage to yield separable joint OAE profiles. Findings in chinchillas will provide mechanistic insight into OAE profile clusters in humans. These data test the sensitivity of joint OAE profiles to specific cochlear dysfunctions and contribute to development of precision diagnostics for SNHL.

Stimulus-frequency otoacoustic emissions and middle-ear pressure gains in a finite-element mouse model.

For evoked otoacoustic emissions (OAEs), the stimulus and emission signals traverse the middle ear (ME) in forward and reverse directions, respectively. In this study, a fully coupled three-dimensional finite-element model of the mouse ear canal (EC), ME, and cochlea was used to calculate ME pressure gains, impedances, and reflectances at the EC-entrance and stapes-footplate-cochlear-fluid interfaces. The cochlear model incorporates a series of interdigitated Y-shaped structures sandwiched between the basilar membrane and reticular lamina, each comprised of a Deiters' cell, its phalangeal-process extension, and an outer hair cell (OHC). By introducing random perturbations to the OHC gains, stimulation-frequency otoacoustic emissions (SFOAEs) were generated. Raising the perturbation magnitude from 10% to 80% increased the SFOAE magnitude by up to 24 dB in the 10-30 kHz frequency range. Increasing or decreasing the stiffness of the stapes annular ligament and eardrum by a factor of 8 changed the SFOAEs by up to 30 dB, but the round-trip ME gain as measured could not account for this. A modified round-trip ME gain, with reflections removed at the EC-entrance and stapes-cochlea boundaries, eliminated a ±10 dB discrepancy and allowed ME changes to be quantitatively associated with changes in measured OAEs.

Usefulness of phase gradients of otoacoustic emissions in auditory health screening: An exploration with swept tones.

Otoacoustic emissions (OAEs) are low-level sounds generated by the cochlea and widely used as a noninvasive tool to inspect cochlear impairments. However, only the amplitude information of OAE signals is used in current clinical tests, while the OAE phase containing important information about cochlear functions is commonly discarded, due to the insufficient frequency-resolution of existing OAE tests. In this study, swept tones with time-varying frequencies were used to measure stimulus frequency OAEs (SFOAEs) in human subjects, so that high-resolution phase spectra that are not available in existing OAE tests could be obtained and analyzed. The results showed that the phase of swept-tone SFOAEs demonstrated steep gradients as the frequency increased in human subjects with normal hearing. The steep phase gradients were sensitive to auditory functional abnormality caused by cochlear damage and stimulus artifacts introduced by system distortions. At low stimulus levels, the group delays derived from the phase gradients decreased from around 8.5 to 3 ms as the frequency increased from 1 to 10 kHz for subjects with normal hearing, and the pattern of group-delay versus frequency function showed significant difference for subjects with hearing loss. By using the swept-tone technology, the study suggests that the OAE phase gradients could provide highly sensitive information about the cochlear functions and therefore should be integrated into the conventional methods to improve the reliability of auditory health screening.

Hearing screening based on deep residual shrinkage network

Stimulus-frequency otoacoustic emissions (SFOAEs) could be a useful tool for assessing hearing capabilities. Training and testing data were collected from 1084 ears of 725 subjects. Based on SFOAEs, this study applied Deep Residual Shrinkage Network to screen hearing status. Results of a 10-fold cross-validation show that the model performed better than other recent literature in the range of 0.5 to 8 kHz, occupied a larger area under the receiver operating characteristic curve (0.970-0.991) and had a higher accuracy (0.932-0.959). The developed classified model outperformed the previous model by accuracy improvements of 1.28% to 4.43% at 0.5, 2, 4 and 8 kHz.

Characterizing the Relationship Between Reflection and Distortion Otoacoustic Emissions in Normal-Hearing Adults.

Otoacoustic emissions (OAEs) arise from one (or a combination) of two basic generation mechanisms in the cochlea: nonlinear distortion and linear reflection. As a result of having distinct generation processes, these two classes of emissions may provide non-redundant information about hair-cell integrity and show distinct sensitivities to cochlear pathology. Here, we characterize the relationship between reflection and distortion emissions in normal hearers across a broad frequency and stimulus-level space using novel analysis techniques. Furthermore, we illustrate the promise of this approach in a small group of individuals with mild-moderate hearing loss. A "joint-OAE profile" was created by measuring interleaved swept-tone stimulus-frequency OAEs (SFOAEs) and 2f1-f2 distortion-product OAEs (DPOAEs) in the same ears using well-considered parameters. OAE spectra and input/output functions were calculated across five octaves. Using our specific recording protocol and analysis scheme, SFOAEs in normal hearers had higher levels than did DPOAEs, with the most pronounced differences occurring at the highest stimulus levels. Also, SFOAE compression occurred at higher stimulus levels (than did DPOAE compression) and its growth in the compressed region was steeper. The diagnostic implications of these findings and the influence of the measurement protocol on both OAEs (and on their relationship) are discussed.

Link between stimulus otoacoustic emissions fine structure peaks and standing wave resonances in a cochlear model.

In response to an external stimulus, the cochlea emits sounds, called stimulus frequency otoacoustic emissions (SFOAEs), at the stimulus frequency. In this article, a three-dimensional computational model of the gerbil cochlea is used to simulate SFOAEs and clarify their generation mechanisms and characteristics. This model includes electromechanical feedback from outer hair cells (OHCs) and cochlear roughness due to spatially random inhomogeneities in the OHC properties. As in the experiments, SFOAE simulations are characterized by a quasiperiodic fine structure and a fast varying phase. Increasing the sound pressure level broadens the peaks and decreases the phase-gradient delay of SFOAEs. A state-space formulation of the model provides a theoretical framework to analyze the link between the fine structure and global modes of the cochlea, which arise as a result of standing wave resonances. The SFOAE fine structure peaks correspond to weakly damped resonant modes because they are observed at the frequencies of nearly unstable modes of the model. Variations of the model parameters that affect the reflection mechanism show that the magnitude and sharpness of the tuning of these peaks are correlated with the modal damping ratio of the nearly unstable modes. The analysis of the model predictions demonstrates that SFOAEs originate from the peak of the traveling wave.

Sexual Dimorphism in the Functional Development of the Cochlear Amplifier in Humans.

Otoacoustic emissions, a byproduct of active cochlear mechanisms, exhibit a higher magnitude in females than in males. The relatively higher levels of androgen exposure in the male fetus are thought to cause this difference. Postnatally, the onset of puberty is also associated with the androgen surge in males. In this study, we investigated sexual dimorphism in age-related changes in stimulus-frequency otoacoustic emissions for children. In a retrospective design, stimulus-frequency otoacoustic emissions were analyzed from a cross-sectional sample of 170 normal-hearing children (4 to 12 years) and 67 young adults. Wideband acoustic immittance and efferent inhibition measures were analyzed to determine the extent to which middle ear transmission and efferent inhibition can account for potential sex differences in stimulus-frequency otoacoustic emissions. Male children showed a significant reduction in otoacoustic emission magnitudes with age, whereas female children did not show any such changes. Females showed higher stimulus-frequency otoacoustic emission magnitudes compared with males. However, the effect size of sex differences in young adults was larger compared with children. Unlike the otoacoustic emission magnitude, the noise floor did not show sexual dimorphism; however, it decreased with age. Neither the wideband absorbance nor efferent inhibition could account for the sex differences in stimulus-frequency otoacoustic emissions. The cochlear-amplifier function remains robust in female children but diminishes in male children between 4 and 12 years of age. We carefully eliminated lifestyle, middle ear, and efferent factors to conclude that the androgen surge associated with puberty likely caused the observed masculinization of stimulus-frequency otoacoustic emissions in male children. These findings have significant theoretical consequences. The cochlea is considered mature at birth; however, the present findings highlight that functional cochlear maturation, as revealed by otoacoustic emissions, can be postnatally influenced by endogenous hormonal factors, at least in male children. Overall, work reported here demonstrates sexual dimorphism in the functional cochlear maturational processes during childhood.

Objective Assessment System for Hearing Prediction Based on Stimulus-Frequency Otoacoustic Emissions.

Stimulus-frequency otoacoustic emissions (SFOAEs) can be useful tools for assessing cochlear function noninvasively. However, there is a lack of reports describing their utility in predicting hearing capabilities. Data for model training were collected from 245 and 839 ears with normal hearing and sensorineural hearing loss, respectively. Based on SFOAEs, this study developed an objective assessment system consisting of three mutually independent modules, with the routine test module and the fast test module used for threshold prediction and the hearing screening module for identifying hearing loss. Results evaluated via cross-validation show that the routine test module and the fast test module predict hearing thresholds with similar performance from 0.5 to 8 kHz, with mean absolute errors of 7.06–11.61 dB for the routine module and of 7.40–12.60 dB for the fast module. However, the fast module involves less test time than is needed in the routine module. The hearing screening module identifies hearing status with a large area under the receiver operating characteristic curve (0.912–0.985), high accuracy (88.4–95.9%), and low false negative rate (2.9–7.0%) at 0.5–8 kHz. The three modules are further validated on unknown data, and the results are similar to those obtained through cross-validation, indicating these modules can be well generalized to new data. Both the routine module and fast module are potential tools for predicting hearing thresholds. However, their prediction performance in ears with hearing loss requires further improvement to facilitate their clinical utility. The hearing screening module shows promise as a clinical tool for identifying hearing loss.

Comparing spontaneous and stimulus frequency otoacoustic emissions in mice with tectorial membrane defects

The global standing-wave model for generation of spontaneous otoacoustic emissions (SOAEs) suggests that they are amplitude-stabilized standing waves and that the spacing between SOAEs corresponds to the interval over which the phase changes by one cycle as determined from the phase-gradient delays of stimulus frequency otoacoustic emissions (SFOAEs). Because data characterizing the relationship between spontaneous and evoked emissions in nonhuman mammals are limited, we examined SOAEs and SFOAEs in tectorial membrane (TM) mutants and their controls. Computations indicate that the spacing between adjacent SOAEs is predicted by the SFOAE phase-gradient delays for TM mutants lacking Ceacam16, where SOAE frequencies are greater than ~20 kHz and the mutants retain near-normal hearing when young. Mice with a missense mutation in Tecta (TectaY1870C/+), as well as mice lacking Otoancorin (Otoa−/−), were also examined. Although these mutants exhibit hearing loss, they generate SOAEs with average frequencies of 11 kHz in TectaY1870C/+ and 6 kHz in Otoa−/−. In these animals, the spacing between adjacent SOAEs is larger than predicted by the SFOAE phase delays. It is also demonstrated that mice do not exhibit the strong frequency-dependence in signal coding that characterizes species with good low-frequency hearing. In fact, a transition occurs near the apical end of the mouse cochlea rather than at the mid-point along the cochlear partition. Hence, disagreements with the standing-wave model are not easily explained by a transition in tuning ratios between apical and basal regions of the cochlea, especially for SOAEs generated in TectaY1870C/+mice.

Human Auditory-Frequency Tuning Is Sensitive to Tonal Language Experience.

Purpose The aim of this study is to investigate whether human auditory frequency tuning can be influenced by tonal language experience. Method Perceptual tuning measured via psychophysical tuning curves and cochlear tuning derived via stimulus-frequency otoacoustic emission suppression tuning curves in 14 native speakers of a tonal language (Mandarin) were compared to those of 14 native speakers of a nontonal language (English) at 1 and 4 kHz. Results Group comparisons of both psychophysical tuning curves (p = .046) and stimulus-frequency otoacoustic emission suppression tuning curves (p = .007) in the 4-kHz region indicated sharper frequency tuning in the Mandarin-speaking group relative to the English-speaking group. The auditory tuning was better at the higher (4 kHz) than the lower (1 kHz) probe frequencies (p < .001). Conclusions The sharper auditory tuning in the 4-kHz cochlear region is associated with long-term tonal language (i.e., Mandarin) experience. Experience-dependent plasticity of tonal language may occur before the sound signal reaches central neural stages, as peripheral as the cochlea.

Maximising the ability of stimulus-frequency otoacoustic emissions to predict hearing status and thresholds using machine-learning models

Objective This study aimed to maximise the ability of stimulus-frequency otoacoustic emissions (SFOAEs) to predict hearing status and thresholds based on machine-learning models. Design SFOAE data and audiometric thresholds were collected at octave frequencies from 0.5 to 8 kHz. Support vector machine, k-nearest neighbour, back propagation neural network, decision tree, and random forest algorithms were used to build classification models for status identification and to develop regression models for threshold prediction. Study sample About 230 ears with normal hearing and 737 ears with sensorineural hearing loss. Results All classification models yielded areas under the receiver operating characteristic curve of 0.926–0.994 at 0.5–8 kHz, superior to the previous SFOAE study. The regression models produced lower standard errors (8.1–12.2 dB, mean absolute errors: 5.53–8.97 dB) as compared to those for distortion-product and transient-evoked otoacoustic emissions previously reported (8.6–19.2 dB). Conclusions SFOAEs using machine-learning approaches offer promising tools for the prediction of hearing capabilities, at least at 0.5–4 kHz. Future research may focus on further improvements in accuracy and reductions in test time to improve clinical utility.

Analyzing Stimulus-frequency Otoacoustic Emission Fine Structure Using an Additive Model.

A good understanding of the origin of stimulus-frequency otoacoustic emission (SFOAE) fine structure in human ears and its probe level-dependency has potential clinical significance. In this study, we develop a two-component additive model, with total SFOAE unmixed into short- and long-latency components (or reflections) using time windowing method, to investigate the origin of SFOAE fine structure in humans from 40 to 70 dB SPL. The two-component additive model predicts that a spectral notch seen in the amplitude fine structure is produced when short- and long-latency components have opposite phases and comparable magnitudes. And the depth of spectral notch is significantly correlated with the amplitude difference between the two separated components, as well as their degree of opposite phase. Our independent evidence for components contributing to SFOAE fine structure suggests that amplitude, phase and delay fine structure in the human SFOAEs are a construct of the complex addition of two or more internal reflections with different phase slops in the cochlea.

Nonlinear reflection as a cause of the short-latency component in stimulus-frequency otoacoustic emissions simulated by the methods of compression and suppression.

Stimulus-frequency otoacoustic emissions (SFOAEs) are generated by coherent reflection of forward traveling waves by perturbations along the basilar membrane. The strongest wavelets are backscattered near the place where the traveling wave reaches its maximal amplitude (tonotopic place). Therefore, the SFOAE group delay might be expected to be twice the group delay estimated in the cochlear filters. However, experimental data have yielded steady-state SFOAE components with near-zero latency. A cochlear model is used to show that short-latency SFOAE components can be generated due to nonlinear reflection of the compressor or suppressor tones used in SFOAE measurements. The simulations indicate that suppressors produce more pronounced short-latency components than compressors. The existence of nonlinear reflection components due to suppressors can also explain why SFOAEs can still be detected when suppressors are presented more than half an octave above the probe-tone frequency. Simulations of the SFOAE suppression tuning curves showed that phase changes in the SFOAE residual as the suppressor frequency increases are mostly determined by phase changes of the nonlinear reflection component.

Relationship Between Behavioral and Stimulus Frequency Otoacoustic Emissions Delay-Based Tuning Estimates.

Purpose The phase delay of stimulus frequency otoacoustic emissions (SFOAEs) has been proposed as a noninvasive, objective, and fast source for estimating cochlear mechanical tuning. However, the implementation of SFOAEs clinically has been thwarted by the gaps in understanding of the stability of SFOAE delay-based tuning estimates and their relationship to behavioral measures of tuning. Therefore, the goals of this study were (a) to investigate the relationship between delay-based tuning estimates from SFOAEs and simultaneously masked psychophysical tuning curves (PTCs) and (b) to assess the across- and within-session repeatability of tuning estimates from behavioral and OAE measures. Method Three sets of behavioral and OAE measurements were collected in 24 normal-hearing, young adults for two probe frequencies, 1 and 4 kHz. For each participant, delay-based tuning estimates were derived from the phase gradient of SFOAEs. SFOAE-based and behavioral estimates of tuning obtained using the fast-swept PTC paradigm were compared within and across sessions. Results In general, tuning estimates were sharper at 4 kHz compared to 1 kHz for both PTCs and SFOAEs. Statistical analyses revealed a significant correlation between SFOAE delay-based tuning and PTCs at 4 kHz, but not 1 kHz. Lastly, SFOAE delay-based tuning estimates showed better intra- and intersession repeatability compared to PTCs. Conclusions SFOAE phase-gradient delays reflect aspects of cochlear mechanical tuning, in that a frequency dependence similar to that of basilar membrane tuning was observed. Furthermore, the significant correlation with PTCs at 4 kHz and the high repeatability of SFOAE-based tuning measures offer promise of an objective, nonbehavioral assay of tuning in human ears.